Iatrogenic hypoglycemia is universally recognized as the number one barrier to the safe, effective management of blood glucose in people with type 1 diabetes (T1D). In previous experiments in the dog, we observed that an increase in liver glycogen content augments counterregulatory hormone secretion during insulin-induced hypoglycemia, thereby increasing hepatic glucose production. The experiments in this proposal will determine to what extant an increase in liver glycogen content can improve hypoglycemic counterregulation in humans with and without T1D. The canine model will be used to improve our understanding of how this comes about. Specific Aim #1 is to determine the effect of increasing liver glycogen deposition on insulin-induced hypoglycemic counterregulation in humans with and without T1D. This question will be addressed by studying two groups of people; one with T1D and one without. Both of these groups will undergo one experiment in which their liver glycogen content will be significantly increased using an infusion of fructose an another in which they receive a saline infusion so as to change liver glycogen only modestly. Then, all subjects will undergo a hypoglycemic/ hyperinsulinemic clamp to determine their counterregulatory responses in the presence and absence of increased liver glycogen content. Hypoglycemia-associated autonomic failure (HAAF) is a temporary condition that affects people with T1D. Therefore, Specific Aim #2 is to determine the effect of increasing liver glycogen deposition on insulin- induced hypoglycemic counterregulation in T1D humans with HAAF. The design of Aim #2 will be similar to that of Aim #1. However, on the day prior to metabolic testing, T1D subjects will undergo a hypoglycemic/ hyperinsulinemic clamp to solicit HAAF. Then, on day 2, the liver glycogen content of each individual will be either increased or remain unchanged, followed by a hypoglycemic/ hyperinsulinemic clamp identical to Aim #1. The final aim will utilize the canine model to more closely examine the mechanisms by which increased liver glycogen content improves hypoglycemic counterregulation. Specific Aim #3 is to determine the importance of insulin-induced hypoglycemia in the brain and in the liver to the improved counterregulatory responses that occur as a result of increased liver glycogen content in the dog. To answer this question we will increase the liver glycogen content of animals and then, during insulin-induced hypoglycemia, selectively make either the head, or the liver euglycemic via glucose infusion, while the rest of the animal's body remains hypoglycemic.